The present invention relates to a vibration actuator that allows lubrication between the roller and the vibrating element of the actuator.
A vibration actuator using ultrasonic vibration is used as a drive actuator for applications that require a high torque and multiple degrees of freedom. Such vibration actuator includes a vibrator such as a piezoelectric element for generating ultrasonic vibration, a vibrating element held in contact with the vibrator, and a roller disposed in contact with the vibrating element. Part of the vibrating element held in contact with the roller is vibrated by complex vibration caused by ultrasonic vibration of the vibrator, and the roller is rotated by friction against such part of the vibrating element. In such actuator in which the roller is rotated while being in contact with the vibrating element, abrasion occurs between the roller and the vibrating element. Thus, there have been various proposals to reduce such abrasion.
Japanese Unexamined Patent Application Publication No. 2008-206251 discloses a vibration actuator having a spherical shaped roller. In the actuator, the vibrator and the vibrating element are connected to form a generally cylindrical shape, and a cylindrical recess is formed on the side of the vibrating element opposite from the vibrator. The roller is disposed in contact with the edge of the recess. The roller is pressed against the vibrating element by a pressing device that is disposed on the side of the roller opposite from the recess. The pressing device has a recess opening toward the roller and storing therein lubricant such as grease. The recess of the vibrating element also stores therein lubricant such as grease. The pressing device and the vibrating element have lubricant supply passages communicating with the respective recesses for replenishment of lubricant from the outside of the respective pressing device and the vibrating element. Thus, lubrication between the pressing device and the roller is accomplished by the lubricant supplied from the recess of the pressing device, and lubrication between the vibrating element and the roller is accomplished by the lubricant supplied from the recess of the vibrating element.
In the actuator disclosed in the publication No. 2008-206251, however, the lubricant storage recess and the lubricant supply passage formed in the respective pressing device and the vibrating element lead to a complicated structure and hence an increased manufacturing time and cost. When the roller has a cylindrical shape instead of the spherical shape and pressed against the vibrating element by the pressing device disposed inside the roller, the structure of the lubricant storage recess becomes more complicated, thereby further increasing manufacturing cost.
The present invention is directed to providing a vibration actuator that allows easy lubrication between the roller and the vibrating element of the actuator.